Phytochelatins (PCs) are small enzymatically synthesized peptides having a general structure of [poly-(gamma-Glu-Cys)n-Xaa] polymers where n equals 2 to 11. They are found in all plant species investigated, a few fungal species, and some marine diatoms, where they act as high affinity metal chelators. In iso-phytochelatins, the polymer is capped C-terminally by a serine, glutamine, glutamic acid or in homo-phytochelatin with beta-alanine.